1. Field of the Invention
This invention, generally, relates to a one-way clutch and, in particular, to a ribbon spring for use in a sprag-synchronzed one-way clutch.
2. Description of the Prior Art
FIG. 1 schematically illustrates the structure of a sprag-synchronized one-way clutch 1. As shown, the sprag-synchronized one-way clutch 1 is to be used as interposed between an inner ring 2 and an outer ring 3 which may rotate coaxially relative to each other. When the inner and outer rings 2 and 3 try to rotate in the opposite directions as indicated by the arrows, the clutch prevents a relative rotation between the inner and outer rings 2 and 3; whereas, when the inner and outer rings 2 and 3 try to rotate in directions opposite to those indicated by the arrows, the clutch allows free relative rotation between the two rings. The sprag-synchronized one-way clutch 1 also includes a pair of ring-shaped outer and inner retainers 4 and 5, each of which is formed with a plurality of sprag insertion holes 4a or 5a as arranged in the circumferential direction at a predetermined pitch. A plurality of sprags 6, each having a specific cross sectional shape which is tapered at the middle and serving as a clutching element between the outer and inner rings 2 and 3, are also provided. Each of the plurality of sprags 6 is disposed as inserted in the corresponding one of the sprag insertion holes 4a and 5a of the outer and inner retainers 4 and 5. Typically, each of the sprags 6 has an outer cam surface 6a, which is defined by one or two radii of curvature, and an inner cam surface 6b, which is defined by a pair of different radii of curvature.
A ribbon spring 7 is disposed between the outer and inner retainers 4 and 5, and moment is normally applied to each of sprags 6 in a predetermined direction by the ribbon spring 7. The ribbon spring 7 is also formed with a plurality of sprag insertion holes 7a at a predetermined pitch, and each of the sprags 6 is inserted into the corresponding one of sprag insertion holes 7a, whereby the sprags 6 are held in position as retained by the ribbon spring 7 approximately at the middle, as shown in FIG 2. The ribbon spring 7 is comprised of a thin plate elongated in shape. After inserting sprags 6 into the insertion holes 7a of the ribbon spring 7, both ends thereof are put together to form a ring, which is then interposed between the inner and outer retainers 4 and 5. As shown in FIG. 2, in an assembled condition, the ribbon spring 7 normally applies a moment to the sprag 6 in a direction indicated by the arrows, so that the sprag 6 is normally biased to be in contact with the inner and outer rings 2 and 3.
The structure of a typical prior art ribbon spring 7 for use in a sprag-synchronized one-way clutch is illustrated in FIGS. 3 and 4. The ribbon spring 7 includes a thin, elongated plate of, for example, stainless steel which is formed with a plurality of sprag insertion holes 7a generally in the shape of a "C" at a predetermined pitch with a tab 7d having a predetermined width projecting into the corresponding insertion hole 7a from one side thereof. It is to be noted that FIG. 4 is a side view of ribbon spring 7 in FIG. 3 showing a partial cross sectional view taken along line I--I indicated in FIG. 3. The ribbon spring 7 includes a pair of side sections 7b, 7b and a plurality of bridging sections 7c arranged along a longitudinal direction at a predetermined pitch as bridging between the pair of side sections 7b and 7b. And, a sprag insertion hole 7a is defined by the pair of side sections 7b and 7b and a pair of bridging sections 7c and 7c. In addition, a tab 7d is formed as a projection projecting into the sprag insertion hole 7a from one side of the corresponding bridging section 7c, and, as a result, the sprag insertion hole 7a is defined generally in the form of letter "C." As shown in FIG. 2, the ribbon spring 7 applies moment to the sprag 6 in a predetermined direction, so that the sprags 6 are biased to be normally in contact with the inner and outer rings 2 and 3. For this reason, it is necessary for the tab 7d to apply a force of an appropriate level to the sprag 6.
As shown in FIG. 5, if for some reason, when the sprag 6 becomes skewed within the sprag insertion hole 7a from the normal position indicated by the dotted line, the contact condition between the sprag 6 and the inner and outer rings 2 and 3 becomes abnormal, so that, during operation, there are brought about various disadvantages, such as wobbling of the sprag 6, excessive wear of the sprag 6 at the portion in contact with the tab 7d, and deformation, damage and popping of the tab 7d, whereby there is a chance that the proper function as a one-way clutch is lost. In order to improve the stabsility of the sprag 6 in the insertion hole 7a, it is conceivable to increase the width W of the tab 7d. However, if the width W of the tab 7d were simply increased, the spring constant of the tab 7d would increase, thereby causing the moment to be applied to the sprag 6 to be excessive which could lead to an increase in dragging torque during idling and the occurrence of breakage due to stress concentration at a corner.
U.S. Pat. No. 4,252,221 issued to Lanzerath et al. on Feb. 24, 1981, proposes to provide a ribbon spring having a plurality of tabss projecting into a sprag insertion window; however, since Lanzerath et al. proposes to provide a center tab which is longer than the other tabs, the sprag tends to be skewed.